Typical glass fiber mat manufacturing operations produce substantial amounts of waste mat. This waste takes the form of edge trim or mat which, for one reason or another, does not meet product specifications. Typically, this waste mat may have a binder content (under or over) which is outside the specifications. Currently, such mat is simply disposed of as waste material. Recovery of the fibers in this waste mat would enable a significant percentage of the cost of its manufacture to be salvaged and eliminate the cost and problems associated with waste mat disposal.
A number of different techniques for recapturing these fibers are possible. One such technique would be to simply chop the binder-containing mat into small nodules and add these nodules to virgin glass fibers to produce a mat. This technique has a number of disadvantages. First, the average fiber length in the recaptured fiber groups will be approximately half that of the virgin fibers as a result of the chopping. Second, these fiber groups will tend to maintain their identity as bundles apart from the remaining virgin fibers, a condition totally unacceptable for most re-use applications.
A second recapture technique is to feed the recaptured fibers directly into the melting furnace with virgin glass batch. The difficulty with this approach is that a major amount of the cost of the fiber is not in the material but, in the cost of production and, by melting the fibers, that amount is lost. In addition, the cost of processing the fibers for feeding to a batch furnace is equal to or greater than the cost of the batch it replaces, making this process economically unattractive.
A third approach is to remove the binder from the fibers and to recycle these recaptured fibers. One such removal technique employs one or more chemicals to chemically reduce the binder for removal. One potential problem with such a method is that the chemical must then, itself, be removed or washed from the fibers with there being some potential for fiber damage, either from the chemical or from the washing process.
An alternate binder removal approach involves heating the binder-containing glass in order to burn out the binder. Care must be taken in this burnout process not to raise the temperature of the fibers to a point near their fusion point which would cause them to bond together into a solid mass, thereby losing their beneficial glass fiber properties. What makes this more difficult to avoid is that the burning out is an exothermic reaction which itself contributes additional heat, elevating the fiber temperature above that which is intended.
A number of patents disclose methods of removing the binder from the glass fibers. Exemplary of the techniques used to date are the following U.S. Patents: U.S. Pat. No. 2,674,549 issued to Balz; U.S. Pat. No. 3,253,897 issued to Falls; U.S. Pat. No. 3,375,155 issued to Adams; U.S. Pat. No. 3,847,664 issued to Gravel; U.S. Pat. No. 3,852,108 issued to Lindberg; and, U.S. Pat. No. 4,145,202 issued to Grodin et al.
None of these patents teach or suggest a method which is appropriate for recapturing fibers from non-woven glass mats quickly and economically. For example, Adams and Balz use chemical oxidizing agents in removing organic binder from the glass fibers. These agents must subsequently be removed by processes which are both costly and time consuming. In the procedures disclosed by Falls and Lindberg, the mat is unsupported during the burnout procedure. While woven fiber mats may have sufficient integrity even without the binder to enable such unsupported handling, non-woven mats do not. Once the binder is removed, a non-woven mat can easily lose its integrity and become a mass of disassociated fibers. Lastly, the processes of Gravel and Grodin et al. partially or totally destroy the fibers by utilizing a pulverization step in their methods prior to burning-out the binder. A substantial percentage of the fibers will be reduced to glass duct. The fibers which are recaptured will be shorter by a significant amount than the virgin fibers to which they will be added, with a corresponding difference in characteristics.
The present invention overcomes these deficiencies of the prior art. More specifically, the present invention discloses a method and apparatus to enable inorganic fibers to be recaptured from scrap mat for recycling by burning off the binder. Further, this method and apparatus enable this burnout procedure to be accomplished in a few seconds rather than in a period of time measured in minutes, as is the case with the prior methods.
In accordance with the instant method, a continuous strip of inorganic fibers such as a waste or scrap mat of non-woven glass fibers is supported and transported through a heating zone where an organic treating material or a compound (which may be, e.g., organic binders, lubricants, resins, etc.) dispersed in the mat, is removed. The mat is supported along a predetermined path in the heating zone so that when the organic treating compound is removed, recyclable or reclaimable fibers may be conveyed in a controlled manner out of the heating zone. The organic treating compound is removed by generating an oxygen-rich heating fluid, conducting the heating fluid to the heating zone and rapidly drawing the heating fluid through the mat at such a mass flow rate (velocity) that excessive temperature build-up is prevented, thus keeping the temperature around the fibers below their incipient fusion point. The heating fluid being drawn through the mat causes the organic treating compound to decompose and removes the products of decomposition or waste gases from the mat, leaving the fibers to be reclaimed or recycled. The clean reclaimable fibers are supported and conveyed from the heating zone. Upon leaving the heating zone the fibers are further conveyed by gravity or by a blast of air or a liquid and thereafter conveyed to either a hydropulper containing virgin fibers or, alternatively, to a dump if the fibers do not meet predetermined standards. Preferably, the incinerated waste gases are combined with the heating fluid being generated to compensate for energy losses. Advantageously, a plurality of layers of mat, e.g., up to five layers of mat may be processed utilizing the present method because the velocity of the heating fluid is kept sufficiently high to prevent heat build-up within the layers, thereby keeping the temperature below the fusion temperature of the glass composition of the fibers in the mat.
The apparatus of the present invention includes means for conveying a continuous strip of inorganic fibers such as scrap or waste fiber glass mat through an enclosed heating zone. A highly porous, rotatable suction drum, operating at a pressure below atmospheric, supports the scrap mat along a predetermined path as it is being conveyed through the heating zone. An oxygen-rich heating fluid, generated in a combustion chamber located distant from the heating zone, is conducted to the heating zone, directed to flow around the rotatable drum and drawn through the foraminous drum and the mat carried thereby, by means of a recirculating fan. The temperature of the heating fluid is maintained at a level high enough to ensure decomposition of the organic treating fluid in the mat while the process temperatures, heating fluid velocity, and speed of rotation of the drum are maintained at levels sufficient to ensure that the fusion or sintering temperature of the glass composition constituting the glass fibers is not reached. The rapidly moving heating fluid not only decomposes the organic treating compound, but also removes the products of decomposition, or waste gases, from the surface of the fibers to be recycled, at a rate sufficient to remove the heat of reaction and prevent excessive temperature build-up, thereby ensuring that the temperature of the reclamation fibers will not reach the fusion temperature of the glass composition. These waste gases may be recycled to the combustion chamber and combined with the heating fluid being generated. Under normal circumstances, the reclaimable or recyclable fibers are dumped via some means into a hydropulper or, if unacceptable quantities of organic treating fluid remain following burnout, the nonreclaimable fibers may be transported into a dump or a scrap bin.
The reclaimed fibers are not significantly damaged by the instant method and apparatus and may be readily dispersed with virgin or new fibers to make an acceptable fiber glass non-woven mat, by a conventional wet-mat process, for example. Alternatively, the reclaimed fibers may be conveyed in mat form from the burnout unit to a binder application and curing unit for binder reapplication.